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Questions from the Past Does weight affect how fast something falls? ►No! ► Fluid friction (Air Resistance) does! ► Which falls faster an elephant or a feather with air resistance. ► If we take away air resistance which will fall faster, the elephant or the feather? ► They will fall at 9.8 m/s2 FORCES What is a force? 1. A force causes a resting object to move, and it can accelerate a moving object by changing the object’s speed or direction. B. Measuring a Force 1. Ex. A spring scale at the grocery store. C. Unit of Force 1. Newtons = the force that is needed to move 1 Kg at a rate of 1 meter per second. 2. Named after Sir Isaac Newton. A. How to Draw Forces Acting on Objects ► 12.1 Forces D. Representing Force 1. Use arrows: a. Direction tells you direction of force. b. Length tells you how much force. I. Sliding Friction 1. Opposes the direction of motion after an object starts moving. 2. Since Sliding friction is less than static friction = less force is needed to keep the object moving Push Sliding friction Rolling friction – opposite force that acts on a rolling object. 1. 100 to 1000 times less than static or sliding friction. K. Fluid friction – friction that acts on an object in water or air. L. Gravity – acts downward to the center of the earth. 1. Gravity causes objects to accelerate downward. M. Push force – force makes you go forward J. Draw and Label the forces acting on a box moving to the left. push Newton’s 3rd Law, ground pushing up gravity Sliding friction An object in motion wants to stay in motion. An object at rest wants to stay at rest. ► Describe Newton’s 1st Law in Your Own Words. When something changes speed or direction it accelerates. ► Describe Law. Newtons 2nd For every action there’s an equal and opposite reaction. ► Describe Law. Newton’s 3rd Guy jumps forward, boat goes backward. A. Gravity D. C. Fluid friction (water) = opposes the velocity fluid friction (wind) = opposes the velocity A. Physical Property ► Any characteristic of a material that can be observed without changing the composition of the material. ► 1. Viscosity– The tendency of a liquid to quit flowing or its resistance to flowing. ► High viscosity = the slower it moves ► Syrup has a higher viscosity than water http://plc.cwru.edu/tutorial/enhanced/lab/visco/intro/intro.htm ► 2. Malleability– The ability of a solid to be hammered without shattering ► Metals are usually malleable. If not, we wouldn’t have gold jewelry or knives! ► Other materials break /shatter when hammered ► 3.Density– Ratio of an object’s mass to volume: Mass/volume (memorize formula!) ► Denser object’s sink and less dense objects float ► The box that has more balls has more mass per unit of volume. This property of matter is called density. ► 4. Hardness– A material’s ability to resist scratching ► Glass is harder than a penny so glass can scratch a penny ► 5. Ductility - The ability of a substance to be stretched; the ability for a metal to be drawn into wire. Protons = Positive part of nucleus ► 1. found in nucleus ► 2. can tell you the exact element Example: if you know the element has 10 protons; you just find element 10 on the periodic table ► Used to find atomic weight Neutrons = no charge ► ► Used to find atomic mass Sometimes the same element can have different numbers of neutrons = ISOTOPES Ex. Carbon 12 has 6 neutrons; 6 protons Carbon 14 has 8 neutrons; 6 protons ► Proton number NEVER changes Electrons = negative ► Atomic number = # of electrons ► Found outside the nucleus ► Weight almost nothing Number of electrons plays no role in calculating the weight of atoms. Valence Electrons ► Electrons outershell found in the Dot Diagrams ► Tell you number of valence electrons ► Chlorine has 7 valence electrons because it has 7 dots around it Atomic number Number of protons Number of Electrons Atomic mass Protons + Neutrons Families ► ► Each column is called a family. Every family has similar characteristics The biggest characteristic is valence electrons The number of valence electrons is represented by Roman numerals above the columns Noble gas have 8 valence electrons even though it has an 0 The Alkali Metals ► Have 1 valence electron…extremely reactive. ► The reactivity increases from the top of Group 1A to the bottom. ► Li, Na, K, Rb, Cs, Fr Alkaline Earth ►2 valence electrons ► Differences in reactivity among the alkaline earth metals are shown by the ways they react with water. ► Be, Mg, Ca, Sr, Ba, Ra The Halogens ►7 valence electrons ► F, Cl, Br, I, At ► Despite their physical differences, the halogens have similar chemical properties. The Noble Gases ► Group 18 ► The noble gases are colorless and odorless and extremely unreactive. ► He, Ne, Ar, Kr, Xe, Rn How Ions are formed! ► ► When an alkali metal or alkaline earth metal bond with a halogen. The alkali metals gives a halogen an electron. The alkali metal becomes a cation (positive) The halogen becomes an anion (negative). Covalent Bonds ► When elements share valence electrons equally!! Law of Conservation of Mass ► Chemical Equations Reactants on left Products on right ► Number of molecules on left has to equal number of molecules on right These equations are said to be balanced. There are six molecules of Carbon on the left, and six on the right. pH Scale ► Tells you how acidic or basic ► Acids Citrus fruits Batteries Stomach juices ► Bases Baking Soda Sea Water Soap Liquid drain cleaner Conductivity ► The ability to allow electricity/heat to flow. ► The more conductivity = the more room electrons have to move. ► Was a test question a couple of years ago…… Kinetic Energy ► Kinetic is moving energy. ► The faster it goes the more energy has ► More temperature = more kinetic energy. Potential Energy ► Potential Energy is essentially height! If it is above the ground is has potential energy. The higher it is the more potential energy it has ► Elastic potential energy If you stretch a substance it has potential energy Law of Conservation of Energy ► Energy can not be created or destroyed. ► Energy is just converted from one form to another. More Energy Transformations Check out how the speed changes as it goes down the hill This was a test question a couple of years ago…. It asked where would the cart be going the fastest…..it goes the fastest at the bottom! Other Energy Conversions ► Energy conversions ► All forms of energy can be converted into other forms. The sun’s energy through solar cells can be converted directly into electricity. Green plants convert the sun’s energy (electromagnetic) into starches and sugars (chemical energy). Fission and Fusion ► Fission is splitting nuclei. Nuclear reactions Nuclear bombs Nuclear powerplants ► Fusion is putting nuclei of atoms together helium reactions in stars Fission This is where the most energy is released. Previous test question…. Fusion Wave Properties III. Properties of Waves A. Frequency, Period, and Amplitude 1. Frequency = # of cycles in a given time 2. Wavelength = is the distance between a point on one wave and the same point on the next cycle of the wave. 3. Amplitude = how high and low the wave goes from the middle. 4. The more energy a wave has, the greater is its amplitude 5. http://www.ngsir.netfirms.com/englishhtm/TwaveA.htm IV. Behavior of Waves A. Reflection = occurs when a wave bounces off a surface it cannot pass through. 1. Reflection does not change the speed or frequency of a wave. ex. When you throw a ball at the wall it bounces back because it can’t go through the wall. Refraction = the bending of a wave as it enters a new medium. 1. When a wave enters a medium at an angle, refraction occurs because one side of the wave moves more slowly than the other side. C. Diffraction = the bending of a wave as it moves around an obstacle or passes through a narrow opening. B. Wave Absorption ► Waves can be absorbed into the medium. Ex. You do not want waves to bounce around in a recording studio. The recording studio walls will have carpet on them to absorb materials. Modern designs are not good for recording studios or music halls. Conduction ► The transfer of heat by direct contact between objects or particles. Convection ► Heat transferred by the movement of molecules within a substance. ► Movement occurs from warmer areas to cooler areas. Radiation ► Heat transferred through space. ► EXAMPLE: The sun’s rays causing a sunburn. Heat/Movement ► Always colder. from warmer to Examples: heat moves from water to ice ► Heat moves from air to water ► Adding more ice to a glass of cold water will just make it get cooler faster and stay cool. Adding more ice does not make something colder! Heat and Particle movement ICE WATER STEAM When you add heat particles move faster! V. Sound and Hearing A. B. C. D. E. Sound waves are longitudinal waves. Sound depends on speed, intensity and loudness, frequency and pitch. Speed = how fast sound travels Intensity = how loud is the sound Frequency = how high it is or how low it is. Wave Superimposing on one Another ► http://www.phy.ntnu.edu.tw/ntnujava/index .php?topic=19